The present invention relates, generally, to sensors, and, specifically, to level sensors for measuring fluid levels in multi-phase fluids.
Measurement of composition of multi-phase fluids, such as emulsions, is an important application in many industries. Determination of oil and water content of emulsions is essential at different stages in the crude oil production and refining stage. Characterization of emulsions is important in oil field management, separators, desalters, wastewater management systems, and oil quality control systems. It is important to know oil and water levels in mixtures obtained from a particular oil field to understand the overall health of the field, as well as to increase productivity and capacity of the field.
In vessel systems such as separators, oil and water and other components present in the emulsion obtained from the well are separated from each other with the help of gravity and a difference of density between different components of the emulsion. In such separators volume of components is determined by observing the interface levels, and using measurement markings on the separator columns. It is also important to measure levels of different components in an emulsion like water-oil at various stages of production of oil from a cost standpoint. Underestimating water content in a particular emulsion can lead to serious cost implications in terms of procurement of additional instruments for separating water from oil. Wastewater management is another application where it is important to characterize emulsions.
To measure oil-water composition in emulsions, demulsifiers are mixed with the emulsion and stirred to separate oil and water in the mixture. Typically, operators visually observe the level of water that gets accumulated to determine levels of water in the emulsion. This technique is prone to human errors and may lead to subsequent errors in selection of demulsifiers required to be used in vessel management systems, waste water management systems and the like.
Many types of level and interface instruments have been contemplated over the years and a subset of those have been commercialized. Among those are gamma-ray sensors, guided wave sensors, magnetostrictive sensors, microwave sensors, ultrasonic sensors, single plate capacitance/admittance sensors, segmented capacitance sensors, inductive sensors, and computed tomography sensors. Each of the sensors has advantages and disadvantages. Some of the sensors are prohibitively expensive for many users. Some of the sensors may require a cooling jacket to perform at operating temperatures (above 125° C.). Some interface instruments require a clear interface to work, which can be problematic when working with diffuse emulsions. Some are susceptible to fouling. Other sensors do not have the ability to provide a profile of the tank, but rather monitor discreet points in the desalting process. Systems using electrodes are susceptible to the shorting of electrodes in high salinity applications and are susceptible to fouling. Finally, many of these systems are complex and difficult to implement.
Some existing sensor systems have used individual capacitive elements to measure fluid levels. A key limitation of those sensor systems is their inability to simultaneously quantify several components in the liquid. Capacitance methods have been used to measure dielectric constant of a liquid using specially designed electrodes for capacitance measurements. These designs are restricted by the need for separate types of electrodes for capacitance measurements and for conductivity measurements. Inductor capacitor circuits also have been used to monitor the fluid level in a container using an electromagnetic resonator where change in capacitance was related to fluid level and fluid type. However, it has been the consensus of those of ordinary skill in the art that the filling of the resonator by a conducting liquid increased the uncertainties and noise in measurements by about one order of magnitude as compared to the values in a non-conducting fluid such as in air. However, these methods do not provide accurate measurements of concentrations of individual analytes at the limits of their minimum and maximum concentrations in the mixture.
With existing sensor systems, no one system is capable of delivering a combination of low cost, high sensitivity, favorable signal-to-noise ratio, high selectivity, high accuracy, and high data acquisition speeds. Additionally no existing system has been described as capable of accurately characterizing or quantifying fluid mixtures where one of the fluids is at a low concentration.
Hence, there is a need for a method and a system that aids in automated measurement of components of a multi-phase fluid.